The present invention relates to an arrangement for the feed of weblike packing material in register with decorations or crease lines present on the packing material web.
In the manufacture of packages, weblike packing material is often used which can be stored in magazine rolls. In automatic packing machines the weblike packing material is converted to filled and closed packing containers, the packing material web being formed to a tube in that the edges of the web are joined together. The tube then is filled with the intended contents and flattened and sealed along narrow sealing zones situated at a distance from one another, these sealing zones extending transversely across the tube. The said sealed tube portions can be shaped to packing containers in connection with or after the sealing by folding of the packing material, and it is customary to impart to the packing container which has been manufactured in the abovementioned manner a parallelepipedic shape by enclosing the lower part of the packing material tube in shaping elements which fold the packing material along crease lines arranged in advance. The crease lines facilitate the folding at the same time as triangular, double-walled lugs are formed at the lower side edges of the packing container.
Since the packing material web in general is provided with a decoration of an advertising or informative character, and also with crease lines to facilitate the folding, it is necessary to advance the packing material tube formed, and hence also the packing material web, with great precision so that the packing decoration will be placed correctly on the packing container and the crease line pattern will coincide with the position of the shaping elements. It is known that such a feed of a packing material web in register with decorations and crease line pattern can be carried out by using so-called folding flaps during the shaping of the abovementioned double-walled triangular lugs, which flaps are formed during the shaping by folding of parallelepipedic containers. The said folding flaps can be made to perform different working motions, that is to press together the triangular lugs to a varying degree depending on the pick-up of a register-holding mark arranged on the packing material web. If more material is to be advanced the flap is moved to its bottom position, otherwise the movement of the flap is stopped before it has reached its bottom position. Such a regulating system is described in Swedish Pat. No. 315.236 and has been found to operate well, but since a small difference in volume will exist between a "compensated" and a "non-compensated" package, the flap movement must not be made too great, since otherwise the volume difference or volume spread may become unacceptable. As the development moves towards more and more rapidly working packing machines, and the increasing speed gives rise to technical problems which means among other things that the capacity of the machine to maintain the decoration diminishes, for example, because of increased acceleration of the paper and movement of the liquid in the tube, the need arises for a safer and better feed regulator.
In accordance with the present invention this technical problem and others are solved with the help of a guide roller driven at variable speed over which the packing material web passes, and by movable elements which are adapted so that they periodically engage the packing material web and advance the web. A further characteristic of the invention are elements for determining the position of the advanced web in relation to the decoration or the crease line pattern arranged on the web, and elements for controlling the speed of the guide roller as a function of the determined web position so that the mechanical tension in the web after the guide roller can be regulated.